PROCESSES FOR OBTAINING SUBSTANCES FROM BARK AND A COMPOSITION CONTAINING BARK FOR USE IN THE PROCESSES

Abstract

Processes for obtaining substances from bark, especially bark high in suberin and lignin, which substances can be used for preparing biofuels are disclosed. The processes use a solvent system for dissolving the substances, which system can be recycled in the process. The solvent system comprises a base selected from tertiary aliphatic amines A composition comprising bark and the solvent system, which can be used in the processes, is also disclosed.

Claims

1. A process for at least partly dissolving in a solvent system substances of bark, which bark contains a suberin component, and for at least partly depolymerising the suberin component, comprising the following steps: providing bark; providing a solvent system comprising water, and a base selected from tertiary aliphatic amines; treating the bark with the solvent system by subjecting the bark to the solvent system at a temperature of at least 160° C., thereby obtaining a composition containing at least partly dissolved substances of bark, of which substances the suberin component is at least partly depolymerised.

2. The process of claim 1, wherein the tertiary aliphatic amine is a simple tertiary aliphatic amine, preferably a trialkylamine, more preferably an amine selected from the group consisting of triethylamine (Et.sub.3N), trimethylamine (Me.sub.3N), dimethylethylamine, and diethylmethylamine, and most preferably triethylamine (Et.sub.3N).

3. The process of claim 1, wherein the bark is Quercus suber (oak) or Betula pendula (birch) bark, preferably Betula Pendula bark.

4. The process according to claim 1, wherein the heating temperature is at least 180° C., and preferably up to 260° C., more preferably at the most 220° C., and most preferably in the range of 200° C. to 220° C.

5. The process according to claim 1, wherein the heating is performed for at least 0.3 hours, preferably for 1 to 3 hours, most preferably for 1.5 to 2.5 hours.

6. The process of claim 1, wherein the solvent system further comprises an alcohol, preferably a low boiling alcohol such as methanol, ethanol, or propanol, or a mixture of low boiling alcohols, most preferably the alcohol is methanol.

7. The process of claim 1, wherein the solvent system comprises: water at a content of at least 40% by volume; triethylamine at a content of 4-20% by volume, preferably 4-15%, more preferably 7-12% by volume; and, methanol at a content of 40-50% by volume of the total volume of the solvent system.

8. The process according to claim 6, wherein the ratio of MeOH:H.sub.2O in the solvent system is from 2:1 to 1:2 v/v.

9. The process according to claim 1, wherein the bark is in the form of finely divided bark, such as milled bark particles, preferably having a particle size of not more than 3 mm, preferably 1 mm or smaller.

10. The process according to claim 1, additionally comprising, after the treatment step, the following step of: recirculating, at least once, the composition obtained after the treatment step, back to the treatment step, for use as solvent system for the next portion of bark to be subjected to treatment conditions in a next treatment step.

11. The process of claim 10, wherein recirculation of the composition obtained after the treatment step us carried out until a total amount of bark has been added to the solvent system corresponding to a lower limit of solvent to bark ratio of V»7 L.Math.kg.sup.−1 has been reached in the composition.

12. The process according to claim 1, additionally comprising, after the treatment step, the step of: subjecting the composition resulting from the treatment step to filtration so as to separate from the composition any solid bark residues.

13. The process according to claim 12, additionally comprising, after the filtration step, the step of: separating by evaporation the solvent system from the composition resulting from the treatment step, and recirculating the separated solvent system for use in the treatment step.

14. A process for preparing a fuel, comprising the following steps: providing bark; providing a solvent system comprising water, an alcohol, and a base selected from tertiary aliphatic amines; treating the bark with the solvent system by subjecting the bark to the solvent system at a temperature of at least 160° C., thereby obtaining a composition containing at least partly dissolved substances of bark, of which substances the suberin component is at least partly depolymerised; subjecting the composition resulting from the treatment step to filtration, so as to separate from the composition any solid bark residues; separating by evaporation the solvent system from the filtrate obtained in the filtration step, so as to obtain a product mixture; and, hydrotreating the product mixture, thereby obtaining a fuel.

15. The process of claim 14, comprising the additional step of: admixing the product mixture to be hydrotreated with, as a carrier liquid, a plant-derived oil, preferably tall oil fatty acid (TOFA) or rapeseed oil.

16. The process of claim 15, wherein the product mixture to be hydrotreated is suspended in the carrier liquid.

17. The process according to claim 14, wherein the hydrotreatment is performed by hydrodeoxygenation.

18. A composition comprising a mixture of bark in a solvent system, the solvent system comprising: water at a content of at least 40% by volume; triethylamine at a content of 4-20% by volume; and methanol at a content of 40-50% by volume, of the total volume of the solvent system.

19. The composition of claim 18, wherein the bark is in the form of finely divided bark, such as milled bark particles, said particles preferably having a particle size of not more than 3 mm.

20. The composition of claim 18, wherein a ratio V of solvent system to bark, in terms of volume of solvent system to weight of bark, is less than >20 l/kg.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0036] In the following, the present invention is explained in more detail, by way of example only, and should not be construed as limiting the scope of protection sought in the appended claims. In this detailed description it is referred to the following figures, wherein:

[0037] FIG. 1 depicts a reaction scheme describing the process steps of preparing biofuel from bark;

[0038] FIG. 2 is a diagram showing the influence of time, temperature, and content of water and triethylamine on bark solubilization;

[0039] FIG. 3A is a diagram showing the results of HSQC NMR analysis of bark-derived gum;

[0040] FIG. 3B is a diagram showing the results of GC-MS analysis of methanolysated bark-derived gum;

[0041] FIG. 4A is a diagram showing the results of a simulated distillation of the bio-oils obtained by the process of the invention; and,

[0042] FIG. 4B is a diagram showing the 2D GC analysis of the distribution of obtained bio-oil components by carbon atom number.

[0043] The present inventors have developed a two-stage process and system for bark conversion into biofuel. According to a preferred embodiment the bark is birch bark. First, in a preferred embodiment, milled birch bark is treated with MeOH—H.sub.2O—Et.sub.3N solvent system in a reactor or the like. The obtained mixture, containing bark solubilized in the solvent system and solid bark residue is filtered. The filtrate may be returned into the same reactor and thus play the role of the next portion of solvent system. The solid bark residue obtained in the filtration is discarded. The filtrate consists mainly of gum, comprising at least partly depolymerized suberin and other substances of bark (“depolymerized bark”) dissolved in the solvent system.

[0044] After several runs of using the gum solution solubilized in the solvent system as solvent for new portions of milled bark, the solvent system MeOH—H.sub.2O—Et.sub.3N is recycled by evaporation and returned to be used again as a pure solvent system consisting of MeOH, H.sub.2O and Et.sub.3N. As a result of the evaporation a semi-solid gum is obtained. This semi-solid gum is subjected to hydrotreatment by hydrodeoxygenation, for example in the presence of a suitable hydrodeoxygenation catalyst, such as Pt/TiO.sub.2/Mo.sub.3, and H.sub.2 gas or HCOOH. This second stage of the process leads to a reaction mixture comprising a variety of different hydrocarbon oils in the diesel-range that may be separated from each other through distillation. The reaction mixture resulting upon hydrotreatment is then distilled in order to obtain different hydrocarbons boiling at different temperatures.

[0045] The inventors of the present invention found that certain amines work surprisingly well in the invention. Ammonia, primary and secondary amines cannot be used because they form amides when reacting with esters.

[0046] For the purpose described herein, the simple tertiary aliphatic amine Et.sub.3N (pKa 10.7) was found to be a surprisingly good choice as a component of the solvent system. In the presence of Et.sub.3N in organosolv pulping conditions, suberin was found to undergo alkaline hydrolysis (cf. FIG. 1A). After the solubilization of the substances of bark in the solvent system has been accomplished, Et.sub.3N can be easily removed by distillation (bp 89° C.) together with other components of the solvent system.

[0047] Mixtures of alcohols with water are suitable for the extraction of nonpolar components of biomass, such as lignin and suberin. Mixtures are more efficient than alcohol or water alone. MeOH can be recycled easier than any other alcohol due to its low boiling point (65° C.).

Optimization of the 1st Stage

[0048] Solubilization of the bark with the MeOH—H.sub.2O—Et.sub.3N solvent system was optimized with regard to minimization of the mass of solid bark residue. The degrees of solubilization (%) are reported in relation to the mass of extractive-free bark (content of EtOH-extractives plus moisture is 29%). As a starting point, we treated the bark with MeOH—H.sub.2O (1:1 v/v or 46 vol. % H.sub.2O) at 220° C. for 1 h in absence of Et.sub.3N, in which conditions only 27% were solubilized (FIG. 2). Addition of 4 vol. % of Et.sub.3N improved the result toward 69%. Increase of Et.sub.3N concentration to 7 vol. % led to 91% solubilization. Further increase (12 vol. %) caused a decline of the solubilization degree (73%).

[0049] Using the optimized Et.sub.3N concentration (7 vol. %), we explored the role of water as component of the solvent system. If no water was added (i.e., Et.sub.3N—MeOH mixture was used as the solvent system), the solubilization degree was lower than in case of MeOH—H.sub.2O 1:1 v/v, but still significant (70%). Addition of 30 vol. % of water did not affect this result (72%). When water became the major component with concentration of 60 vol. %, the degree of solubilization hits the maximum (93%). A H.sub.2O—Et.sub.3N solvent system without MeOH led to a small decline of the result (89%) and was more difficult to handle during filtration. Therefore, if the content of water is higher than 46 vol. % its change does not affect the process. We decided to use 46 vol. % of water because presence of MeOH makes recycling of the solvent system as well as other operations such as filtration easier.

[0050] We also investigated the effect of temperature. When the process was carried out for 1 h with the optimized solvent system (MeOH—H.sub.2O, 1:1.7 vol. % Et.sub.3N) at 160° C., very poor solubilization was observed (13%). Increase of the temperature afforded better results: from 45% at 180° C. to 54% at 200° C. and, finally, 91% at 220° C.

Solvent System Recycling (Evaporation)

[0051] The solvent system was recycled 3 times by distillation in vacuum. The recycling and bark solubilization data are presented in Table 1 below. Composition of the solvent system after each recycling step was determined by NMR in acetone-d.sub.6. It was observed that concentration of Et.sub.3N slightly decreases at each step, therefore it makes sense to start with higher concentrations of Et.sub.3N (˜10%) when optimizing the process for industry. The recycled solvent was used for solubilization of new samples of bark. The data were in accordance with the obtained during optimization.

TABLE-US-00001 TABLE 1 Recycling of the solvent system by evaporation Solvent system composition Solvent system Bark Number (vol. %) recovery (wt. %) solubilization of run Et.sub.3N MeOH H.sub.2O [compared to initial mass] (wt. %) 1 7 47 46 94 [94] 91 2 6 49 45 99 [93] 92 3 6 48 46 99 [92] 87 4 6 40 54 — 89

Solvent System Recycling (No Evaporation)

[0052] Due to the low density of bark packing in a reactor (150 kg.Math.m.sup.−3), the lower limit of solvent system to bark ratio is V≈7 L.Math.kg.sup.−1. It was found that until that point, for V=20, 15, 10 and 7 L.Math.kg.sup.−1, solubilization degree does not depend on this parameter, coming to 91, 92, 91 and 90%, respectively. Handling is more convenient with larger ratio V. However, evaporation of solvent system demands a sufficient amount of energy, ˜1.7 MJ per liter of the solvent system. Therefore, and also because solvent system recycling by evaporation causes a slight decline of the yield (cf. Table 1), it would be beneficial to decrease V by using the solvent system several times before evaporation, i.e. using the solution for processing each portion of bark like in a looped flow system. Indeed, the presence of bark components in the solution did not affect its ability to solubilize new portions of bark: in three consecutive experiments with V=10 L.Math.kg.sup.−1, degrees of solubilization came to 91%, 90%, 90%. Thus, the efficient solvent system to bark ratio was reduced to 3.3 L.Math.kg.sup.−1. It must be noticed that filtration slows down significantly with each time as the solution becomes more concentrated and viscous, and it might lead to problems when putting the process on industrial scale.

Analysis of Gum

[0053] The gum obtained by “bark depolymerization” (i.e. bark wherein suberin component of bark has been at least partly depolymerized) contains a variety of oligomeric products of suberin and lignin cleavage. M.sub.W=2630 Da, M.sub.N=932 Da (PD=2.8), according to SEC data, i.e. an average dissolved molecule is composed of 4-5 monomeric units of lignin and/or suberin. Elemental composition of the material differs insignificantly from the composition of bark, however 1-2% of residual nitrogen is present. The material is insoluble in hexane, moderately soluble in toluene (28% of the gum weight) and well soluble in methanol (87% of the gum weight).

[0054] Noteworthy, the gum forms a suspension in tall oil fatty acid (TOFA) at 120° C. which remains practically stable at room temperature, therefore TOFA can be used as a carrier liquid in an industrial process of the gum hydrotreatment. Viscosity of the suspension at room temperature is 15-500 m.Math.Pas for the concentration range 7-33 wt. % and temperature range 25-70° C.

[0055] HSQC NMR (cf. FIG. 3A) demonstrated presence of typical structural motifs of suberin. In order to analyze monomeric fatty acids, the gum was subjected to alkaline methanolysis, and the extract was studied by means of GC (FIG. 3B). A variety of C.sub.16-C.sub.22 hydroxylated carboxylic acids and diacids was identified, with the main components being 22-hydroxydocosanoic (26% TIC as silylated derivatives) and 1,18-octadec-9-enedioic (14%) acids. In addition, ferulic acid (3%) was detected.

Hydrodeoxygenation. Simdis and 2D GC

[0056] The gum was subjected to hydrodeoxygenation in the presence of Pt/MoO.sub.3/TiO.sub.2 catalyst at 360° C. Simulated distillation study of the obtained bio-oil showed that it contains hydrocarbons within the diesel range. The lightest components have boiling points of 70° C. and 90% of the mixture boils away before 350° C. (FIG. 4A).

[0057] 2D GC technique allowed to study different types of components of the mixture (FIG. 4B). The most abundant molecules are C.sub.15-C.sub.19 hydrocarbons. In the natural suberin, only fatty acids with even carbon atom numbers are present. Therefore, hydrocarbons with uneven chain length emerge due to cracking and/or decarboxylation processes. Higher aromatic compounds such as naphthalenes (20 wt.% ) are probably also the products of cracking since their carbon atom numbers are generally lower than the ones of other observed hydrocarbons (average 14.4 versus 16.8 for the whole mixture). Unsaturated and monounsaturated hydrocarbons account for up to 73 wt. %, however, due to the presence of aromatic compounds the average number of double bonds and/or cycles per molecule for the whole mixture is 2.4 and H/C ratio is 1.83.

[0058] Yield of the obtained bio-oil is 40% of initial bark weight (56% of extractive-free bark). Carbon content in the bio-oil is 86%, as calculated through 2D GC data, and the carbon yield (the ratio of carbon which has been transferred from bark to the product) is 62%. Various types of bio-oil components and their content are presented in Table 2.

TABLE-US-00002 TABLE 2 Various types of bio-oil components and their content Number-average Component wt. % carbon atom number n-Alkanes 24.1 18.2 Branched alkanes 23.4 18.5 Alkenes 25.1 17.2 and cycloalkanes Alkylbenzenes 7.7 16.3 Higher aromatics 19.7 14.4 Whole mixture 100.0 16.8

Experiment 1

1. Analysis of the Bark Feedstock

[0059] The bark of birch (Betula pendula) was analysed.

1.1. Extractives & Moisture

[0060] A sample of bark was extracted with EtOH in Soxhlet extractor for 12 h and then dried in air at 50° C. for 12 h. Weight loss: 29% of bark weight. Mass of the EtOH-solubilized material: 26% of bark weight.

1.2. Suberin

[0061] Extractive-free bark sample (0.347 g) was treated with 3% MeONa solution in MeOH (25 mL) under reflux for 2 h. The solution was centrifugated and the residue was washed with MeOH and water. Centrifugation and washing were repeated until the pH became neutral. Solid residue was dried (0.131 g, 38% of extractive-free bark, 27% of total). Solution was acidified to pH 3 with H.sub.2SO.sub.4 and extracted with DCM (3×10 mL). The organic fraction was dried, filtered and concentrated to afford suberin oil (0.160 g, 46% of extractive-free bark, 33% of total).

1.3. Lignin

[0062] The solid residue which remained after alkaline methanolysis (extractive-free desuberized bark) was dried in air at 70° C. for 12 h. A sample (91 mg) was treated with 72% aqueous H.sub.2SO.sub.4 (1 mL) at 30° C. for 1 h. Then the mixture was diluted with water (30 mL) and refluxed for 3 h. After cooling to rt, the mixture was filtered through paper filter. The filter was washed with water until a neutral pH was reached, and the residue was dried in air at 70° C. for 12 h to afford acid-insoluble lignin (51 mg, 21% of extractive-free bark, 15% of total).

1.4. Lignin S/G Ratio

[0063] A sample of untreated bark (50 mg) was placed into a stainless-steel reactor together with 3% aqueous KOH (3 mL) and nitrobenzene (0.1 mL). The reactor was heated with stirring at 170° C. for 1 h. After cooling, the mixture was acidified with HCl to pH 1 and extracted with DCM (3×5 mL). Combined organic fraction was dried with Na.sub.2SO.sub.4, diluted with Et.sub.2O and subjected to GC-MS. Method: Syringol and guaiacol units were detected as syringaldehyde and vanillin. Though the reproducibility of the method is low, syringol to guaiacol ratio was determined to be 2.2-2.7 based on three runs.

1.5. Carbohydrates

[0064] Analysis for carbohydrates was carried out according to previously published procedure; Kumaniaev, I.; Subbotina, E.; Sävmarker, J.; Larhed, M.; Galkin, M. V.; Samec, J. S. M. Lignin depolymerization to monophenolic compounds in a flow-through system. Green Chem. 2017, 19, 5767-5771. No carbohydrates were detected.

[0065] The results of the analysis of composition of the birch bark feedstock used are presented in Table 3 below.

TABLE-US-00003 TABLE 3 Composition of birch bark feedstock Moisture  3% EtOH extractives 26% Suberin, hydrophilic monomers 11% Suberin, hydrophobic monomers 33% Klason lignin 15% Balance 88%

1.6. Elemental Analysis

[0066] The direct elemental analysis by combustion was performed on the birch bark feed stock. The following results were obtained: C, 70.1%; H, 9.2%; N, 0.3%; O, 19.5%.

2. Solubilization of Bark (Stage 1)

2.1. Experimental Procedure

[0067] Grinded birch bark (˜1 mm particle size, 0.30 g) was placed into a stainless-steel reactor (internal volume 7 mL) together with a mixture of triethylamine (0.35 mL), methanol (2.32 mL) and water (2.33 mL) and a magnetic stirring bar. The reactor was heated at 220° C. in an oil bath for 2 hours with 800 rpm stirring. After cooling, the mixture was filtered through paper filter. The solid residue was dried at 60° C. for 12 hours and weighted (0.02 g, 6% of initial bark weight). The filtrate was distilled to recover the solvent system. The residual brown gum was dried in air at 60° C. or 130° C. for 12 hours (0.28 g, 94% of initial bark weight) and subjected to analyses.

2.2. Optimization

[0068] The procedure was optimized with regard to minimization of weight of the solid residue. Each experiment was repeated at least twice to address possible issues of samples' heterogeneity. The experimental data of these experiments are presented in Table 4 below. For graphical representation of the results, see FIG. 2.

TABLE-US-00004 TABLE 4 Bark solubilization in MeOH—H.sub.2O—Et.sub.3N Solvent system Solvent volume, system mL (mL % solubilized (MeOH—H.sub.2O—Et.sub.3N) per g of (of wax-free Deviation, # v/v bark) T, ° C. Time, h Bark, g bark) % (+/−) 1 46:47:7 4.5 (15) 200 0.3 0.30 34 4 2 46:47:7 4.5 (15) 200 0.5 0.30 38 5 3 46:47:7 4.5 (15) 200 1.0 0.30 54 3 4 46:47:7 4.5 (15) 200 2.0 0.30 58 9 5 46:47:7 4.5 (15) 200 3.0 0.30 77 0 6 46:47:7 4.5 (15) 160 0.5 0.30 13 0 7 46:47:7 4.5 (15) 180 1.0 0.30 45 0 8 46:47:7 4.5 (15) 220 1.0 0.30 79 1 9 46:47:7 4.5 (15) 220 2.0 0.30 91 1 10 48:48:4 4.5 (15) 220 2.0 0.30 69 1 11 50:50:0 4.5 (15) 220 2.0 0.30 27 1 12 44:44:12 4.5 (15) 220 2.0 0.30 73 2 13 62:31:7 4.5 (15) 220 2.0 0.30 72 1 14 31:62:7 4.5 (15) 220 2.0 0.30 93 0 15 0:93:7 4.5 (15) 220 2.0 0.30 89 3 16 93:0:7 4.5 (15) 220 2.0 0.30 70 1 17 46:47:7  4.5 (7.5) 220 2.0 0.60 90 2 18 46:47:7 4.5 (10) 220 2.0 0.45 91 4

2.3. NMR spectroscopy

[0069] 0.1 g of the gum was suspended in 0.6 mL of CDCl.sub.3 at 60° C., the mixture was cooled to room temperature without filtration and subjected to NMR analysis. The spectra were recorded with a Bruker 400 (400 MHz) spectrometer as solutions in CDCl.sub.3. Chemical shifts are expressed in parts per million (ppm, δ) and are referenced to CHCl.sub.3 (δ=7.26 ppm) as an internal standard. .sup.13C NMR spectra were recorded as solutions in CDCl.sub.3 with complete proton decoupling. Chemical shifts are expressed in parts per million (ppm, δ) and are referenced to CDCl.sub.3 (δ=77.0 ppm) as an internal standard. 2D-NMR spectra were acquired on an Agilent 400-MR spectrometer. The standard Agilent implementations of gHSQCAD experiments were used. The results of the NMR spectroscopy analysis are presented in FIG. 3A.

2.4. Size Exclusion Chromatography

[0070] Size exclusion chromatography (SEC) was performed using a YL 9110 HPLC-GPC system with three Styragel columns (HR 0.5, HR 1, and HR 3, 7.8×300 mm each) connected in series (flow rate: 1 mL.Math.min.sup.−1; injection volume: 50 μL; THF), a UV detector (254 nm), and an auto-sampler. The system was calibrated using ReadyCal-Kit poly(styrene) (Mp 266, 682, 1250, 2280, 3470, 4920, 9130, 15700, 21500, 28000, 44200, 66000 Da). Samples were dissolved in THF to a concentration of 0.5 gL.sup.−1.

[0071] The detected oligomers possess the following properties:

[0072] Molecular weight of the most abundant species M.sub.P=1584 Da

[0073] Number average molecular weight M.sub.N=932 Da

[0074] Weight average molecular weight M.sub.W=2630 Da

[0075] Polydispersity index PD=M.sub.W/M.sub.N=2.82

TABLE-US-00005 TABLE 5 Solubility of the bark gum in various solvents (ca. 0.05 g in 1 mL) Concentration of Solvent Gum dissolved, wt % the solution, g .Math. L.sup.−1 Hexane 0 0 Toluene 28 16 Ethyl acetate 65 33 Methanol 87 48

2.5. Elemental Analysis

[0076] Gum dried at 60° C. in air: C, 66.7%; H, 10.2%; N, 2.1%; O, 21.4%.

[0077] Gum dried at 130° C. in air: C, 71.4%; H, 9.9%; N, 1.1%; O, 17.2%.

2.6. Tests for Solubility of the Gum

[0078] Solubility of the gum in various organic solvents was measured as follows. The gum (0.05 g) was treated with a solvent (1 mL) at 60-70° C. for 30 min, the solution was cooled 20° C. and filtered through a 0.2 μm syringe filter. Mass of the filtrate was measured. Then the filtrate was concentrated in vacuum and the residue dried in air at 60° C. for 12 hours. Mass of the residue was measured. The results of the tests on solubility of the bark gum in various solvents are presented in Table 5 below.

2.7. Suspension of the Gum in Tall Oil

[0079] Tall oil is a naturally occurring liquid mixture of fatty acids and rosins which has been demonstrated to be useful carrier liquid for hydrotreatment of biomass derivatives. For this purpose, viscosity of the mixture is crucial. The gum forms a suspension in tall oil fatty acids mixture (TOFA) at 120° C. which remains practically stable at room temperature. Viscosity of the suspension was measured with Anton Paar Rheolab QC rotational rheometer with a CC10 sensor (stirring rates 50 to 1400 s.sup.−1). The viscosity data of the gum suspension in TOFA at different temperatures and concentrations is given in Table 6.

TABLE-US-00006 TABLE 6 Viscosity of the gum suspension in TOFA at different temperatures and concentrations (mPa .Math. s) 25° C. 50° C. 70° C.  7 wt. % 13 <10 <10 16 wt. % 120 35 <10 33 wt. % 500 125 44

2.8. 1D GC-MS of the Gum Methanolysate

[0080] 1D GC was used for analysis of monomeric composition of the gum. A sample of the gum (0.1 g) was refluxed with 3% KOH/MeOH (5 mL) for 1 h. The mixture was acidified with HCl, diluted with water and extracted with CHCl.sub.3 (3×10 mL). Combined organic phases were dried with Na.sub.2SO.sub.4, filtered and concentrated. A sample of the residue (10-20 mg) was dissolved in THF (1 mL) and silylated with bis(trimethylsilyl)acetamide (50 μL) in the presence of pyridine (50 μL). The solution was subjected to GC. GC measurements were performed on a Shimadzu Shimadzu GC-MS-QP2020 equipped with a HP-5 MS capillary column (30 m×0.25 mm×0.25 μm) and an MS detector. Compounds were identified by comparing the observed fragmentation patterns to literature data. MS spectra of each identified derivative are given in FIG. 3B.

Conclusions from Experiment 1

[0081] The inventors of the present invention have thus surprisingly found and shown in Example 1 that MeOH—H.sub.2O—Et.sub.3N (46/47/7% v/v) forms a salt- and metal-free solvent system that is recyclable and affords to solubilize bark of birch (Betula pendula) to the degree of 94% (91% of wax-free bark). The obtained gum is composed of organosolv lignin and suberin oligomers and was characterized with HSQC NMR, elemental analysis, gas chromatography, and size exclusion chromatography. Hydrotreatment of the gum affords a hydrocarbon oil of diesel range (40% yield, bp 271° C., H/C=1.83, theoretical higher heating value 45-48 MJ.Math.kg.sup.−1) which was studied by means of simulated distillation and 2D GC.

Itemized Listing of Examples of Aspects and Embodiments of the Invention

[0082] Item 1: A composition comprising bark and a solvent system, wherein the substances of bark are at least partly dissolved in the solvent system, and of which substances the suberin component of bark is at least partly depolymerised, and wherein the solvent system comprises water, and a base in the form of an amine.

[0083] Item 2: The composition of item 1, wherein the aliphatic amine is a tertiary aliphatic amine.

[0084] Item 3: The composition of item 2, wherein the tertiary aliphatic amine is a simple tertiary aliphatic amine, preferably triethylamine (Et.sub.3N), trimethylamine (Me.sub.3N), dimethyl ethyl amine, diethyl methyl amine, most preferably triethylamine (Et.sub.3N).

[0085] Item 4: The composition of any one of items 1-3, wherein the solvent system further comprises an alcohol, preferably a low boiling alcohol such as methanol, ethanol, or propanol, or a mixture of low boiling alcohols, most preferably the alcohol is methanol.

[0086] Item 5: The composition of any one of items 1-4, wherein the degree of solubilization of the bark in the solvent system is at least 65%, preferably at least 90% and more preferably 90-95%.

[0087] Item 6: The composition of any one of items 1-5, comprising a variety of oligomeric products of the suberin and/or lignin, each molecule being composed of 4-10 monomeric units of lignin and/or suberin, and the whole mixture having the number-average molecular weight 900 Da and the weight-average molecular weight 2600 Da, according to SEC data.

[0088] Item 7: The composition of any one of items 1-6, wherein the bark after further treatment in alkaline conditions affords a mixture of fatty acids having a chain length of 18-22 carbons, the fatty acids being saturated or unsaturated, and optionally substituted by at least one hydroxy group.

[0089] Item 8: The composition of any one of items 1-7, wherein the mixture of fatty acids includes at least two of 18-hydroxyoctadec-9-enoic acid, 1,18-octadec-9-enedioic acid, 1,18-octadecanedioic acid, 20-hydroxyeicosanoic acid, 1,20-eicosanedioic acid, 1,22-docosanedioic acid, 9,10-dihydroxyoctadecane-1,18-dioic acid, and 22-hydroxydocosanoic acid.

[0090] Item 9: The composition of any one of items 1-8, wherein the bark is bark having a high content of suberin and lignin, such as Quercus suber (oak) or Betula pendula (birch) bark, preferably Betula Pendula bark.

[0091] Item 10: A process for preparing a composition of any one of items 1-8, comprising treating finely divided bark with the solvent system as defined in any one of items 1-9 in order to at least partly depolymerise the suberin component of bark.

[0092] Item 11: The process of item 10, wherein the treatment with the solvent system is performed at a temperature of at least 160° C. to obtain bark dissolved in the solvent system.

[0093] Item 12: The process of any one of items 10 and 11, wherein the treatment temperature is at least 180° C., preferably at the most 220° C., and most preferably in the range of 200° C. to 220° C.

[0094] Item 13: The process of any one of items 10 to 12, wherein the heating is performed for at least 0.3 hours, preferably for 1 to 3 hours, most preferably for 1.5 to 2.5 hours.

[0095] Item 14: The process of any one of items 10 to 13, wherein the ratio of MeOH:H.sub.2O in the solvent system is from 2:1 to 1:2 v/v.

[0096] Item 15: The process of any one of items 10 to 14, wherein the bark is in the form of finely divided particles, preferably milled bark particles preferably having a particle size of not more than 3 mm, preferably 1 mm or smaller.

[0097] Item 16: The process of any one of items 10 to 15, wherein the bark is bark having a high content of suberin and lignin, such as Quercus suber or birch bark, preferably birch bark.

[0098] Item 17: The process of any one of items 10 to 16, wherein the composition obtained as a result of the depolymerisation reaction performed on the finely divided bark in the process is subjected to filtration and any solid bark residues are separated and discarded.

[0099] Item 18: The process of any one of items 10 to 17, wherein the filtrate obtained by the filtration is recycled at least once and used as solvent for the next portion of bark to be subjected to depolymerisation conditions for at least partly depolymerising the suberin component in the bark.

[0100] Item 19: The process of any one of items 10 to 18, wherein the solvent system after completion of the depolymerisation treatment of the bark for depolymerising at least partly the suberin component in the finely divided bark is separated from the resulting reaction mixture by evaporation and recycled for use as solvent system for new portions of finely divided bark to be subjected to depolymerisation treatment for depolymerising at least partly the suberin component.

[0101] Item 20: A mixture comprising a variety of oligomeric products of suberin and lignin, each molecule being composed of 4-10 monomeric units of lignin and/or suberin.

[0102] Item 21: The mixture according to item 20 comprising fatty acids having a chain length of 18-22 carbons, the fatty acids being saturated or unsaturated, and optionally substituted by at least one hydroxy group.

[0103] Item 22: The mixture according to item 21, the mixture of fatty acids including at least two of 18-hydroxyoctadec-9-enoic acid, 1,18-octadec-9-enedioic acid, 1,18-octadecanedioic acid, 20-hydroxyeicosanoic acid, 1,20-eicosanedioic acid, 1,22-docosanedioic acid, 9,10-dihydroxyoctadecane-1,18-dioic acid, and 22-hydroxydocosanoic acid.

[0104] Item 23: A composition suitable for preparation of fuel, comprising a mixture according to anyone of items 20-22 and a carrier liquid suitable for use in fuel preparation.

[0105] Item 24: The composition according to item 23, wherein the carrier liquid is a plant-derived oil, such as tall oil fatty acid (TOFA) or rapeseed oil.

[0106] Item 25: The composition according to item 24, wherein the composition is a suspension of said mixture in TOFA.

[0107] Item 26: A process for preparing fuel, comprising a step of hydrotreating the mixture of anyone of the items 20-22 or the composition of anyone of the items 23-25.

[0108] Item 27: The process according to item 26, wherein the hydrotreatment is performed by hydrodeoxygenation.

[0109] Item 28: The process according to item 26 or 27, wherein the hydrotreatment produces C.sub.9-C.sub.27 hydrocarbons, preferably C.sub.15-C.sub.19 hydrocarbons.

[0110] Item 29: The process according to any one of items 26 to 28, wherein the process prior to the hydrotreatment step incorporates the steps of the process according to anyone of the items 10-19.

[0111] Item 30: A biofuel obtainable by the process of anyone of the items 26 to 29.